Gain control systems and methods for controlling an adjustable power level

ABSTRACT

A system, such as a transceiver, for controlling an adjustable power level includes first and second power detectors, a network of attenuators, a compensator, a comparator, and a controller. The first power detector measures the power of a signal. The network of attenuators receives the signal and generates an attenuated signal. The compensator receives the attenuated signal and generates a compensated signal. The second power detector measures the power of the compensated signal. The comparator receives the respective outputs from the first and second power detectors and generates a first error signal. The controller enables the fixed attenuation, correspondingly adjusts the variable attenuation, receives a second error signal, and provides a control signal to the network of attenuators to nullify an attenuation mismatch introduced between the fixed attenuation and the variable attenuation. A corresponding method for controlling an adjustable power level is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2010/029261, filed Mar. 30, 2010, the benefit of the filing dateof which is hereby claimed and the specification of which isincorporated herein by this reference.

BACKGROUND

As the designs of portable radio frequency (RF) communication devices,such as cellular telephones, personal digital assistants (PDAs), WIFItransceivers, and other mobile communication devices evolve, suchdevices must be capable of adjusting transmitted power accurately over arelatively wide dynamic range. For example, in the emerging markets of3G/3.9G, linear systems such as those that communicate in accordancewith standards such as WCDMA, WiMAX, EUTRAN-LTE, and other non-constantenvelope modulation methodologies, the requirements for those standardsfor accurate transmitted power control continue to present challenges.

In mobile communication systems, power control is implemented to ensurethat the power level of communication signals arriving at a base stationfrom various mobile devices are relatively the same. To accomplish thisgoal, the base station continuously monitors the received signal powerfrom each mobile device communicating with the base station. The basestation directs each mobile device to adjust the transmit power leveldepending upon its distance, data rate change, or channel condition. Thethird generation partnership project (3GPP) specification calls for amaximum output power for a mobile handset of 24 dBm. A minimum outputpower for a mobile handset is −57 dBm. The difference between 24 dBm and−57 dBm results in a dynamic range of transmitted power of 81 dB.Providing such a dynamic range in a mobile communication device is not adifficult task. However, the 3GPP specification further includes aspecification for transmit power step tolerance that with smallercommanded step sizes step sizes in transmit power becomes morestringent. A transmit power step tolerance describes a range ofacceptable power levels in response to a base station commandcommunicated to the mobile communication device that directs the deviceto adjust its transmit power. Table I below illustrates the transmitpower step tolerance in accordance with the 3GPP specification. Forexample, when the base station directs the mobile communication deviceto increase transmitted power by 3 dB, the mobile communication deviceis required to increase transmitted power by 1.5 dB to 4.5 dB. Asindicated in the first line of Table I, when no change in transmittedpower is commanded by the base station, the transmitted power from themobile communication device is required to not increase or decrease bymore than 0.5 dB.

TABLE I TRANSMITTED POWER POWER STEP SIZE ΔP(DB) STEP TOLERANCE (DB) 0±0.5 1 ±0.5 2 ±1.0 3 ±1.5  4 ≦ ΔP ≦ 10 ±2.0 11 ≦ ΔP ≦ 15 ±3.0 16 ≦ ΔP ≦20 ±4.0 21 ≦ ΔP ±6.0

A conventional transmitter includes a combination of three variableattenuators. Generally, two of the variable attenuators are connected inseries with a third variable attenuator connected between the first twoattenuators in shunt to ground (e.g., a “T” attenuator). Attempts tocontrol the output power by controllably adjusting the attenuationprovided by the variable attenuators to provide the transmitted powerstep tolerance of the 3GPP specification are problematic in that theyrequire factory calibration to adjust for production tolerances andtemperature variation over a relatively wide range of operationaltemperatures for the separate independent attenuation stages.

SUMMARY

Embodiments of a gain control system and a method for controlling anadjustable power level eliminate gain discontinuities when generatingadjacent adjustable gain states over a select portion of a range ofadjustable gain states by selectively applying one or more fixed gainelement(s) and correspondingly adjusting one or more variable gainelement(s). The gain control system and method for controlling anadjustable power level provide a more accurate and continuous powerlevel transfer function when compared to factory calibration solutionswhich can fail when a transceiver is operating under a host of changingconditions in the field.

An embodiment of a gain control system includes first and second powerdetectors, a network of attenuators, a compensator, and a comparator.The first power detector measures the power of a signal and provides afirst power detector output. The network of attenuators includes a fixedattenuation and a variable attenuation. The network of attenuatorsreceives the signal and provides an attenuated signal. The compensatorreceives the attenuated signal and amplifies the same in an amountproximate to the fixed attenuation to generate a compensated signal. Thesecond power detector measures the power of the compensated signal andprovides a second power detector output. The comparator receives thefirst power detector output and the second power detector output andgenerates a first error signal.

An embodiment of a method for controlling an adjustable power levelusing a network of attenuators that includes a fixed attenuation and avariable attenuation, includes the steps of using a controller to adjustthe variable attenuation until the attenuation of the variableattenuation approaches an attenuation of the fixed attenuation, using acompensator at an output of the network of attenuators to provide gainto an attenuated signal in an amount proximate to the fixed attenuationto generate a compensated signal at a compensator output, in acomparator, measuring a difference between a first power level of anon-attenuated signal and a second power level of the compensated signalto generate a first error signal and storing the first error signal.

Other systems, methods, features, and advantages will be or will becomeapparent to one with skill in the art upon examination of the followingfigures and detailed description. It is intended that all suchadditional systems, methods, features, and advantages be included withinthis description, be within the scope of and protected by theaccompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The gain control systems and methods for controlling an adjustable powerlevel can be better understood with reference to the following figures.The components within the figures are not necessarily to scale, emphasisinstead being placed upon clearly illustrating the principles of how toeliminate gain discontinuities when selecting adjacent adjustable gainstates over a select portion of a range of adjustable gain states.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a block diagram of an embodiment of a simplified portabletransceiver including a gain control system.

FIG. 2 is a schematic diagram of an embodiment of the gain controlsystem of FIG. 1.

FIG. 3 is a schematic diagram of an embodiment of the network ofattenuators of FIG. 2.

FIG. 4 is a schematic diagram of a more detailed embodiment of the gaincontrol system of FIG. 2 before fixed attenuation is enabled.

FIG. 5 is a schematic diagram of a more detailed embodiment of the gaincontrol system of FIG. 2 after fixed attenuation is enabled.

FIGS. 6A-6B include a flow diagram illustrating an embodiment of amethod for controlling an adjustable power level using the gain controlsystem of FIG. 1.

DETAILED DESCRIPTION

Although the exemplary embodiments are described in relation to aportable RF transceiver, and more specifically a transmitter in aportable RF transceiver, embodiments of the present gain control systemsand methods for controlling an adjustable power level can be applied inany application where a continuous and adjustable output power isdesired.

The gain control systems and methods for controlling an adjustable powerlevel can be implemented in hardware, software, or a combination ofhardware and software. When implemented in hardware, the gain controlsystems and methods for controlling an adjustable power level can beimplemented using specialized hardware elements and logic. When the gaincontrol systems and methods for controlling an adjustable power levelare implemented partially in software, the software portion can be usedto control components in a transmitter or a power amplifier controlelement so that various operating aspects can be software-controlled.The software can be stored in a memory and executed by a suitableinstruction execution system (e.g., a microprocessor). The hardwareimplementation of the gain control systems and methods for controllingan adjustable power level can include any or a combination of thefollowing technologies, which are all well known in the art: discreteelectrical components, amplifiers, comparators, a discrete logiccircuit(s) having logic gates for implementing logic functions upon datasignals, an application specific integrated circuit having appropriatelogic gates, a programmable gate array(s) (PGA), a field programmablegate array (FPGA), etc.

The software for controlling components in a transmitter, such as a gaincontrol system, comprises an ordered listing of executable instructionsfor implementing logical functions, and can be embodied in anycomputer-readable medium for use by or in connection with an instructionexecution system, apparatus, or device, such as a computer-based system,processor-containing system, or other system that can retrieve theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions.

In the context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer-readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. More specific examples (a non-exhaustive list) ofthe computer-readable medium would include the following: an electricalconnection (electronic) having one or more wires, a portable computerdiskette (magnetic), a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), and a portable compact disc read-only memory (CDROM) (optical).Note that the computer-readable medium could even be paper or anothersuitable medium upon which the program is printed, as the program can beelectronically captured, via for instance optical scanning of the paperor other medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory.

A combination of elements that generate a negative gain (e.g.,radio-frequency attenuators) can be arranged with a compensator (e.g.,an amplifier or amplifiers) capable of generating an output with asubstantially equivalent positive gain to offset signal power loss in afixed attenuation to provide nearly continuous control of a signal powerlevel over a desired range of signal power levels. One or more fixed RFattenuators can be arranged in a circuit. A switch in parallel with eachof the respective one or more fixed RF attenuators can be controllablyclosed to bypass the attenuation provided by a respective RF attenuator.One or more variable RF attenuators can be added to the circuit. Avariable RF attenuator is a circuit element with negative gain thatvaries as a function of a signal parameter applied at a control signalinput. If the variable attenuation (i.e., the range of the negativegain) is greater than the attenuation of a fixed RF attenuator, acontrol solution can be arranged to avoid discontinuity in the power ofa signal that traverses the circuit. A network of RF attenuatorsincluding at least one fixed attenuator and a variable attenuator, powerdetectors, a compensator, a comparator and a controller, as well as oneor more converters, can be configured or controllably updated as desiredto adjust a variable RF attenuator in a network of RF attenuators toremove discontinuities in transmitted power over a broad range oftransmit signal power.

The example gain control systems and methods smooth or reduce outputpower level discontinuities that are introduced when fixed and variableRF attenuators are switched or otherwise adjusted to provide a stepchange in attenuation. The attenuation provided by the fixed RFattenuator is offset by a compensator, which applies a substantiallyequivalent positive gain to an attenuated version of the transmitsignal. For example, if the fixed RF attenuator provides 10 dB ofattenuation to the received signal (i.e., a pre-attenuation signal),then the compensator provides 10 dB of gain. A transmit signal power ismonitored at an input of the gain control system. The transmit signal(i.e., a post-attenuation signal) is adjusted by the compensator tooffset the attenuation introduced by the fixed RF attenuator. Thesepre-attenuation and post-attenuation signals are compared to generate afirst error signal that is forwarded to a controller. After enabling thefixed attenuation and reducing the variable attenuation by asubstantially equivalent attenuation to that provided by the fixedattenuator(s), the gain control system measures the power of thepre-attenuation and compensated post-attenuation signals to generate asecond error signal. The controller generates a control signal inresponse to a function of the first error signal and the second errorsignal. In this way, the controller, through the control signal, adjuststhe variable RF attenuator to reduce any discontinuities in signal powerintroduced in the network of attenuators.

The gain control system, as shown in the following exemplaryembodiments, can achieve a practical attenuation range of 2*(Att_Fx),where Att_Fx represents the attenuation of the fixed RF attenuator. Thecontrolled attenuation range can be extended by another (Att_Fx) byswitching in an additional fixed RF attenuator, introducing anadditional compensator gain G in an amount substantially equal to theattenuation of the additional fixed RF attenuator, and repeating thesame process at the next switching point. Additional variable attenuatorstages are not needed.

In general, the attenuation range can be extended by N*(Att_Fx) byadding N additional fixed attenuators and N additional compensator gainsto the gain control system. Each time, the adjustment is performed inthe following order. The variable attenuation starts close to zero andis increased until it is about equal to the attenuation introduced byone fixed attenuator or Att_Fx, at which point the error signalapproaches zero and the bypass switch for the next fixed attenuator isopened while the variable attenuation is simultaneously reduced byAtt_Fx (dB). The variable attenuator is adjusted until the error isunchanged from its value before the switch. Thereafter, anothercompensator with a gain of G (dB), where G is approximately equal toAtt_Fx is enabled to prepare for the next cycle. This process could berepeated with additional fixed attenuators and compensator gains, thepractical limit being where the total attenuation becomes so great thatthe compensator output becomes too noisy to rely on.

Although described in association with an increase in attenuationprovided by a network of attenuators, it should be understood that thegain control system and methods apply equally to decreases inattenuation. That is, as the variable attenuator is directed to provideless variable attenuation, the controller will determine when it isappropriate to remove a fixed attenuation provided by a fixed attenuatorand replace the fixed attenuation with a substantially equivalentvariable attenuation. A comparison of the error signal values generatedbefore and after the change in the network of attenuators can be used togenerate a control signal to further adjust the variable attenuator toreduce discontinuities in signal power introduced in the network ofattenuators.

In accordance with an illustrative or exemplary embodiment of the gaincontrol systems and methods for controlling an adjustable power level,FIG. 1 includes a block diagram illustrating a simplified wirelesscommunication system 100 including a gain control system 200. Thewireless communication system 100 includes a baseband subsystem 110, aninput/output (I/O) element 112, a transmitter 130, a front-end module140, an antenna 145, and a receiver 150. The I/O element 112 is coupledto the baseband subsystem 110 via connection 114. The I/O element 112represents any interface with which a user may interact with thewireless communication system 100. For example, the I/O element 112 mayinclude a speaker, a display, a keyboard, a microphone, a trackball, athumbwheel, or any other user-interface element. A power source (notshown), which may be a direct-current (DC) battery or other powersource, is also connected to the baseband subsystem 110 to provide powerto the wireless communication system 100. In a particular embodiment,the wireless communication system 100 can be, for example but notlimited to, a portable-telecommunication device such as a mobilecellular-type telephone.

The baseband subsystem 110 includes microprocessor (g) 115 and memory116. The microprocessor 115 and the memory 116 are in communication witheach other. Depending on the manner in which the baseband subsystem 110controls the transmitted power level emitted from the wirelesscommunication system 100, the baseband subsystem 110 may also includeone or more of an application-specific integrated circuit (ASIC), afield programmable gate array (FPGA), or any otherimplementation-specific or general processor, among other devices.

The baseband subsystem 110, via microprocessor 115 and the memory 116,provides the signal timing, processing, input, output, and storagefunctions for the wireless communication system 100. In addition, thebaseband subsystem 110 generates various control signals, such as powercontrol signals, filter control signals, and modulator control signalsthat are used to direct various functions within the transmitter 130,the front-end module 140, and the receiver 150 as known to those skilledin the art. The various control signals may originate from themicroprocessor 115 or from any other processor within the basebandsubsystem 110, and are supplied to a variety of connections within thetransmitter 130, the front-end module 140, and the receiver 150. Itshould be noted that, for simplicity, only the basic components of thewireless communication system 100 are illustrated herein.

If portions of the gain control system 200 and the methods forcontrolling an adjustable power level are implemented in software thatis executed by the microprocessor 115, the memory 116 will also includegain control software 118. The gain control software 118 comprises oneor more executable code segments and or data values that can be storedin the memory 116 and executed in the microprocessor 115. Alternatively,the functionality of the gain control software 118 can be coded into anASIC (not shown) or can be executed by an FPGA (not shown), or anotherdevice. The functionality of the gain control software 118 can also beprovided by a suitably configured controller in the gain control system200 of the transmitter 130. Because the memory 116 can be rewritable andbecause a FPGA is reprogrammable, updates to the gain control software118 including gain stages or ranges, data, etc. can be remotely sent toand saved in the wireless communication system 100 when implementedusing either of these methodologies.

In one embodiment, the gain control software 118 includes one or moreexecutable code segments for generating power step commands that areforwarded to the gain control system 200. The gain control software 118operates in response to power control commands received from a remotebase station. Example power control commands direct the mobilecommunication device 100 to increase or decrease emitted power. Examplepower step commands generated in the baseband subsystem 110 and receivedby the gain control system 200 may include an indicator and a relativevalue in dB. The indicator directs the gain control system 200 toincrease or decrease transmit signal power. The relative value definesthe desired step change in emitted power. The baseband subsystem 110 mayinclude additional software, firmware or other elements that operate inconjunction with transmitter elements other than the gain control system200 to further adjust the power of an RF signal emitted from the mobilecommunication device 100. Exemplary transmitter elements include mixers,filters, power amplifiers, attenuators (other than those in the gaincontrol system 200), among other elements that can affect the emittedpower of a RF signal transmitted from the mobile communication device100.

As will be explained in greater detail in association with the detaileddescription of the embodiment of the gain control system 200 shown inFIG. 2, the baseband subsystem 110 will, at appropriate times,communicate power step change commands to the gain control system 200.Moreover, the arrangement and operation of the gain control system 200will be further explained in association with the functional blockdiagrams of FIGS. 2-5.

The transmitter 130 includes a modulator (not shown), which modulatesthe analog signals and provides a modulated signal to an upconverter(not shown). The upconverter transforms the modulated signal on to anappropriate transmit frequency and provides the upconverted signal to apower amplifier (not shown). The power amplifier amplifies theupconverted signal to an appropriate power level for the communicationprotocol or standard in which the wireless communication system 100 isdesigned to operate. The modulated, upconverted, amplified, andgain-controlled transmit signal is forwarded to front-end module 140 viaconnection 132. The gain control system 200 is introduced to dynamicallyand selectively manage transitions in the transmitted power that resultfrom controlled adjustment of fixed and variable RF attenuators in thetransmitter 130 of the wireless communication system 100.

The front-end module 140 comprises an antenna system interface that mayinclude, for example, a diplexer having a filter pair that allowssimultaneous passage of both transmit signals and receive signals inrespective frequency ranges, as known to those skilled in the art. Thetransmit signal is supplied from the front-end module 140 to the antenna145 for signal transmission to suitably configured communicationdevices, such as a base station, remote from wireless communicationsystem 100.

A signal received by an antenna 145, from the base station or otheremitter, is directed from the front-end module 140 to the receiver 150via connection 142. The receiver 150 includes various components todownconvert (i.e., translate in frequency), digitize, and filter arecovered data signal from a receive signal, as known to those skilledin the art. A mixing stage downconverts and separates the received RFsignal into in-phase (I) and quadrature-phase (Q) receive signals. The Iand Q receive signals are sampled and transformed into digital signalsby one or more analog to digital converters (ADCs). One or morespecialized digital filters are introduced to further process the I andQ received signals.

The transmitter 130 and the receiver 150 may be co-located in anintegrated transceiver, such as when the transmitter 130 and thereceiver 150 are implemented on a radio-frequency (RF) integratedcircuit (IC). In alternative embodiments, the receiver 150 and thetransmitter 130 are implemented on separate ICs. Under botharchitectures, the gain control system 200 is preferably implemented inhardware on an integrated circuit in the transmitter 130.

FIG. 2 is a block diagram of an embodiment of the gain control system200 of FIG. 1. In the illustrated embodiment, the gain control system200 includes a first detector 210, a network of attenuators 220, acompensator 230, a second detector 240, a comparator 250, and acontroller 260. The gain control system 200 receives an input signal onconnection 205 and generates an output signal on connection 225. Anetwork of attenuators 220 is connected in series between the connection205 and the connection 225. The network of attenuators 220 includes afixed attenuator (not shown) that provides a fixed attenuation and avariable attenuator (not shown) that provides a variable attenuation.The network of attenuators 220 generates an attenuated signal onconnection 225.

In the illustrated embodiment, the connection 205 is coupled to anin-phase/quadrature phase modulator or IQ modulator (not shown) in thetransmitter 130 of the portable transceiver 100 (FIG. 1). In alternativeembodiments, the input signal could be coupled to any signal generatorwhere it is desirable to adjust output signal power such that steptransitions in output signal power are closely controlled.

The first detector 210 receives the input signal on connection 205 andprovides a first detector output on connection 213 to the low-passfilter 215. The first detector output is a signal that is a function ofthe total signal power received from the I/Q modulator on connection205. A first low-pass filter 215 receives the output from the firstdetector 210 on connection 213. The low-pass filter 215 reduces themagnitude of signal components received via connection 213 from thefirst detector 210 that have a frequency above a cutoff frequency of thefilter. The low-pass filter 215 can be implemented as an active filteror a passive filter. An active filter can comprise a circuit of passivecircuit elements (e.g., resistors, capacitors, or inductors) in one ormore feedback paths of an amplifier. A passive filter will include anarrangement of passive circuit elements. The cutoff frequency of thelow-pass filter 215 can be controllably adjusted by varying one or moreof the resistances, capacitances, or inductances of the passive elementsof the filter as is well known in the art. However implemented oradjusted, the low-pass filter 215 forwards on connection 217 a filteredrepresentation of the first detector output to a first input of thecomparator 250.

The compensator 230 receives the attenuated signal on connection 225.The compensator provides gain or amplifies the attenuated signal in anamount that approximates the amount of attenuation provided by the fixedattenuator from the network of attenuators 220 to generate a compensatedsignal, which is coupled on connection 233 to the second detector 240.

The second detector 240 receives the compensated or gain adjusted signalon connection 233 and provides a second detector output on connection243 to the low-pass filter 245. The output from the second detector 240is a signal proportional to the power of the signal received from thecompensator 230. The signal proportional to the signal power receivedfrom the compensator 230 is forwarded on connection 243 to the low-passfilter 245. The low-pass filter 245 reduces the magnitude of signalcomponents received via connection 243 from the second detector 240 thathave a frequency above a cutoff frequency of the filter. The low-passfilter 245 can be implemented as an active filter or a passive filter.An active filter can comprise a circuit of passive circuit elements(e.g., resistors, capacitors, or inductors) in one or more feedbackpaths of an amplifier. A passive filter will include an arrangement ofpassive circuit elements. The cutoff frequency of the low-pass filter245 can be controllably adjusted by varying one or more of theresistances, capacitances, or inductances in the passive elements of thefilter as is well known in the art. However implemented or adjusted, thelow-pass filter 245 forwards on connection 247 a filtered representationof the second detector output to a second input of the comparator 250.

The comparator 250 receives the first detector output on a first inputalong connection 217 and the second detector output on a second inputalong connection 247. The comparator 250 generates an error signal,which is forwarded on connection 253 to an analog-to-digital converter(ADC) 255 before being forwarded to the controller 260 on connection257. The error signal is a function of the difference of the signalvoltages present at the first and second inputs of the comparator 250.

The controller 260 receives a digital representation of the error signalon connection 257 from the ADC 255. As described above, the controller260 is coupled to a fixed attenuator in the network of attenuators 220via an enable/disable signal, which the controller 260 provides onconnection 263 and a control signal, which the controller 260 provideson connection 265. In the illustrated embodiment, the controller 260 isa digital element that includes a memory 262. The memory 262 can hold orstore the error signal for comparison with a subsequent error signal. Aswill be explained in greater detail below, the controller 260 generatesthe control signal on connection 265 as a function of a first or storederror value and a second or subsequent error signal received onconnection 255. Since the controller 260 is a digital element, thecontrol signal on connection 265 is a digital word that is translated bythe digital-to-analog converter (DAC) 270 into an analog value that isforwarded on connection 275 to a variable attenuator in the network ofattenuators 220.

The controller 260 is enabled and operates in accordance with one ormore signals provided from the baseband subsystem 110 via bus 120. Forexample, there are two main ranges of power control for a 3G mobiletransmitter. In a first or high-power control range (e.g., a transmitsignal power of approximately +5 dBm to +24 dBm, measured at antenna145) the controller 260 may be disabled or turned off after configuringthe network of attenuators 220. In this first or high-power controlrange, the network of attenuators 220 can be bypassed entirely orotherwise configured to provide little or no attenuation while thetransmitted power level is adjusted by controlling the gain of a poweramplifier (not shown). In this high-power mode, the transmitter outputpower can be measured using a diode detector (not shown) at the poweramplifier output. In a second or low-power control range (e.g., lessthan about +5 dBm at antenna 145), the controller 260 is enabled orpowered on. In this case, the power amplifier gain is a constant, andthe output power of the power amplifier is out of range of the diodedetector, which can no longer provide a reliable measure of the outputpower. So, power control is achieved in the low-power control range bycontrolling the input power to the power amplifier, i.e., by adjustingthe total attenuation provided by the network of attenuators 220. Inaccordance with the schedule provided in Table I, only relative accuracyis required (i.e., accurate step changes in signal power). The gaincontrol system 200 accomplishes an accurate step change in emittedsignal power in a manner that eliminates attenuation discontinuitiesthat would otherwise degrade the step accuracy.

When the required transmit power step tolerance provides for a greatertolerance (see Table I), the controller 260 could be applied in an openloop control mode absent compensation or error information. When atighter step tolerance is required, gain compensated error informationcan be provided to the controller 260 to keep the change in error signalvalues relatively small.

Because the error signal is generated as a result of a comparison ofpower-adjusted signals, accuracy requirements of the amount of the gain,G, of the compensator 230, the attenuation (Att_Fx) of the fixedattenuator 322, and offsets in the first detector 210, the seconddetector 240, and the comparator 250 are relatively low.

FIG. 3 is a schematic diagram of an embodiment of the network ofattenuators 220 of FIG. 2. In the illustrated embodiment, the network ofattenuators 220 includes a series arrangement of a fixed attenuator 322and a variable attenuator 324 forming a transmit signal path. That is,the network of attenuators 220 is connected between an I/Q modulator(not shown) and a power amplifier (not shown). The fixed attenuator 322is coupled at its input and output by a switch 325, which operates inaccordance with an enable/disable signal provided from the controller260 on connection 263. Although the fixed attenuator 322 is implementedin the illustrated embodiment as a single attenuator, it should beunderstood that in alternative embodiments, the fixed attenuation couldbe implemented via a combination of several independently bypassableattenuators and in other alternative embodiments could further includeone or more shunting branches associated with one or more of theindependently bypassable attenuators as may be desired. Moreover, thecompensated gain could be made programmable and adjusted to match aprogrammable attenuator (e.g., in a digital circuit implementation inwhich the programmable attenuator is adjusted by a digital controlsignal). Depending on the desired accuracy of the steps in theprogrammable version of the compensator, an automatic gain control curvecould be provided by testing the compensator during manufacture. Inaddition, such a modified gain control system could be used to determinea compression point introduced by an output signal amplifier. Thecompression point could be identified by monitoring the gain of theoutput stage over an increase in the signal power provided to the outputstage.

In embodiments that change the negative gain provided by the fixedattenuation a corresponding change to the gain provided by thecompensator 230 is desired. By way of example, if a modified network ofattenuators provides for fixed attenuation steps of 3 dB, 6 dB, and 12dB, a modified compensator should be inserted that providescorresponding amounts of gain to the transmit signal to cancel theapplied fixed attenuation. Stated another way, when 3 dB of fixedattenuation is applied, the compensator 230 provides 3 dB of gain.Similarly, when 6 dB of fixed attenuation is applied, the compensator230 provides 6 dB of gain.

In accordance with a disable condition defined by the controller 260,the switch 325 is closed and an input signal from the I/Q modulator (notshown) on connection 205 bypasses the fixed attenuator 322 and iscoupled to an input of the variable attenuator 324. When the switch 325is closed, the total attenuation provided by the network of attenuators220 is equal to the attenuation of the variable attenuator 324 and anattenuated representation of the input signal is forwarded on connection225 to the power amplifier (not shown).

In accordance with an enable condition, the switch 325 is opened and aninput signal on connection 205 is attenuated by an amount equal to thatprovided by the fixed attenuator 322 and the attenuation of the variableattenuator 324. The enable condition can be set in conjunction with apower control schedule stored in a memory 262 in communication with thecontroller 260 (FIG. 2) that calls for a transition in the transmittedor output signal power. To provide a smooth step transition in overallgain (i.e., negative gain or attenuation), the controller 260 isconfigured to decrease the attenuation provided by the variableattenuator 324 by an amount close to the attenuation of the fixedattenuator 322 when the fixed attenuator 322 is introduced to the signalpath. That is, the variable attenuator 324 is adjusted to decrease itsattenuation by an amount that approximates the attenuation of the fixedattenuator 322 at a time corresponding to the opening of the switch 325.Thus, the controller 260 (FIG. 2) is configured to keep the totalattenuation provided by the network of attenuators 220 unchanged whenthe above-described switch and configuration adjustment is accomplishedin the network of attenuators 220.

Consider the situation where the network of attenuators 220 is directedby the controller 260 to provide a total attenuation that exceeds theattenuation range of the variable attenuator 324. When this is the case,the controller 260 will provide a suitable signal on connection 263 toopen the switch 325 and add the attenuation provided by the fixedattenuator 322 to the transmit signal path. Substantiallysimultaneously, the controller 260 will provide a suitable signal onconnection 275 to reduce the attenuation provided by the variableattenuator 324 by the amount of attenuation introduced by the fixedattenuator 322. Thereafter, the controller 260 can further adjust thecontrol signal on connection 275 to provide or remove attenuation toemit the desired transmit power from the mobile communication device100.

An attenuation mismatch occurs when the attenuation provided by thefixed attenuator 322 does not match the attenuation removed by adjustingthe variable attenuator 324. Attenuation mismatches can occur because ofcomponent variation in the fixed attenuator 322 and the variableattenuator 324 as a result of manufacturing variation as well as changesin these components over time, temperature, and frequency. The gaincontrol system 200 reduces discontinuities in the attenuation providedin a network of attenuators 220 in the transmit signal path.

As described below in association with the embodiment illustrated inFIGS. 4 and 5, the gain control system 200 measures and records a firsterror value before the fixed attenuation is enabled. The gain controlsystem 200 measures a second error value after the fixed attenuation isenabled and the variable attenuator is correspondingly adjusted. Thus,the overall negative gain (or attenuation in the network of attenuators220 before and after enabling the fixed attenuator 322) will besubstantially the same. The controller 260 further adjusts the variableattenuator in accordance with a function of the first error value andthe second error value to reduce power discontinuities due toattenuation mismatches and to a lesser extent variation in the variableattenuator over time, temperature and frequency. The gain control system200 can repeatedly measure and record error values and applies the sameto a function to generate a control signal that adjusts the network ofattenuators 220 when the mobile communication device 100 is operating inthe above-described low-power control range and accurate stepadjustments are desired.

Should a difference occur between a first error value and a second orsubsequent error value due to an attenuation mismatch, the subsequenterror signal will be different from the stored error signal value in thememory 262 associated with the controller 260. The controller 260compares the stored error value with the subsequent error value andmodifies the control signal on connection 265 to reduce an attenuationmismatch introduced between the variable attenuator 324 and the fixedattenuator 322 at a transition in a power control schedule or in theabsence of such a transition to more accurately adjust the variableattenuator 324 to achieve a desired step change in emitted power withinthe required tolerance provided in Table I.

FIG. 4 is a schematic diagram of a more detailed embodiment of the gaincontrol system of FIG. 2 before fixed attenuation is enabled. As furtherindicated in the illustrated embodiment, the compensator 230 (FIG. 2)can be implemented by an amplifier 430 with a gain, G, that approximatesthe magnitude of the attenuation (Att_Fx) provided by the fixedattenuator 322. In addition, each of the detectors 210, 240 (FIG. 2) canbe implemented by a respective diode detector 410, 440, and thecomparator 250 (FIG. 2) can be implemented by a circuit including anoperational amplifier 450 with a reference or inverting input coupled tothe connection 217 and a signal or non-inverting input coupled to theconnection 247.

The gain control system 200′ is represented before fixed attenuation isenabled. That is, the switch 325 is closed and the input signal followsthe bypass path 423. As indicated in FIG. 4, an input signal having apower, “a,” as provided on connection 205, is detected by diode detector410 to generate a signal on connection 213 that is a function of thesignal power “a.” The signal that is a function of the signal power “a”is then low-pass filtered by filter 215 and forwarded on connection 217to the reference or inverting input of the operational amplifier 450.Before the fixed attenuator 322 is introduced to the gain control system200′, the signal at the input to the compensator 430 is the differenceof “a” (the input signal power) and the power loss in the variableattenuator or “a−Att_Var1.” The signal that is a function of the signalpower “a” and the attenuation “Att_Var1” provided by the variableattenuator 324 is gain adjusted by the amplifier 430 before being senton connection 233 to the diode detector 440. The diode detector 440generates a signal on connection 243 that is a function of the gainadjusted signal power on connection 233. Thus, the gain adjusted signalthat is a function of the signal power “a” and the attenuation“Att_Var1” provided by the variable attenuator 324 is low-pass filteredby filter 245 and forwarded to the signal or non-inverting input of theoperational amplifier 450. Thus, the signal detected by diode detector440 is the signal power of the input signal less the attenuation of thevariable attenuator but including the gain G of amplifier 430, such thatat the signal or non-inverting input of the operational amplifier 450 isthe difference of the input signal power and the sum of power loss inthe variable attenuator and the increase in signal power or gainprovided by the compensator 230, shown here as “a−Att_Var1+G.”Accordingly, the error signal on connection 253 at the output of theoperational amplifier 450 can be represented by “G−Att_Var1.” Asdescribed above, the error signal (i.e., a signal (i.e., a first errorsignal) on connection 253 is sampled and digitized in ADC 255. Thedigitized representation of the first error signal is forwarded onconnection 257 to the controller 260, where it can be stored in asuitable location in memory 262 for subsequent processing by thecontroller 260.

FIG. 5 is a schematic diagram of a more detailed embodiment of a gaincontrol system 200″ after fixed attenuation is enabled. That is, theswitch 325 is opened. As indicated in FIG. 5, an input signal having apower, “a,” as provided on connection 205, is detected by diode detector410 to generate a signal on connection 213 that is a function of thesignal power “a.” The signal that is a function of the signal power “a”is then low-pass filtered by filter 215 and forwarded to the referenceor inverting input of the operational amplifier 450 on connection 217.After the fixed attenuator 322 is introduced to the gain control system200″, the signal at the input to the compensator 430 is the differenceof “a” (the input signal power) and the power loss in the fixedattenuator 322 and the power loss in the variable attenuator or“a−Att_Fx−Att_Var1.” The signal that is a function of the signal power“a” and the total attenuation “Att_Fx+Att_Var1” provided by the fixedattenuator 322 and the variable attenuator 324 is gain adjusted by theamplifier 430 in an amount substantially equivalent to the attenuationloss Att_Fx due to the fixed attenuator 322 before being sent onconnection 233 to the diode detector 440. Thus, the gain adjusted signalthat is a function of the signal powers “a” and the total attenuation“Att_Fx+Att_Var1” is provided on connection 243 to the filter 245. Theoutput of the low-pass filter 245 is forwarded on connection 247 to thesignal or non-inverting input of the operational amplifier 450. Thus,the signal detected by diode detector 440 is the signal power of theinput signal less the total attenuation of the fixed and variableattenuators 322, 324 but including the gain G of amplifier 430, suchthat at the signal or non-inverting input of the operational amplifier450 is the difference of the input signal power and the sum of powerloss in the fixed and variable attenuators 322, 324 and the increase insignal power or gain provided by the compensator 230, shown here as“a−Att_Fx−Att_Var2+G.” Accordingly, the error signal on connection 253at the output of the operational amplifier 450 can be represented by“G−Att_Fx−Att_Var2.” As described above, the error signal (i.e., asecond error signal) on connection 253 is sampled and digitized in ADC255 and forwarded on connection 257 to the controller 260. The seconderror signal and the previously stored first error signal are applied bythe controller 260 in a logical function to generate a suitable controlword which is communicated on connection 265 to the DAC 270. In turn,the DAC 270 generates an analog control signal that is forwarded onconnection 275 to a control input of the variable attenuator 324.

FIGS. 6A-6B include a flow diagram illustrating an embodiment of amethod 600 for controlling an adjustable power level that can beimplemented by the gain control system 200. The flow diagram shows thearchitecture, functionality, and operation of the gain control system200 wherein a network of attenuators 220 including a fixed attenuator322 that provides a fixed attenuation and a variable attenuator 324 thatprovides a controlled and variable attenuation are controllably bypassedand/or adjusted, respectively, to modify signal power over at least aportion of the dynamic range of an emitted power transmitted from themobile communication device 100. In this regard, one or more blocksrepresent the functions of circuit elements in the gain control system200.

The method 600 begins with block 602 where a controller 260 is used toadjust a variable attenuation (e.g., the variable attenuator 324) untilthe attenuation provided by the variable attenuator 324 approaches anattenuation of a fixed attenuation (e.g., the attenuation provided bythe fixed attenuator 322) in a network of attenuators 220. In block 604,a compensator 230 at an output of a network of attenuators 220 is usedto provide signal gain in an amount proximate to the fixed attenuationto generate a compensated signal at a compensator output. Preferably,the compensator 230 provides a gain or amplification of an attenuatedsignal in an amount that approximates the amount of attenuation providedby the fixed attenuator 322 in the network of attenuators 220. Asattenuation is required to adjust the output power level, the variableattenuator 324 is adjusted until the attenuation of the variableattenuator 324 approaches the attenuation of the fixed attenuator 322 inthe network of attenuators 220 Thereafter, as indicated in block 606, acomparator 250 or an operational amplifier 450 is used to measure adifference between a first power level of a non-attenuated signal and asecond power level of the compensated signal to generate a first errorsignal. In input/output block 608, the first error signal is stored in amemory (e.g., memory element 262) coupled to the controller 260.

As indicated by the connector labeled “A,” the method continues withblock 610 in FIG. 6B where the controller 260 introduces the fixedattenuation (e.g., by communicating an enable/disable signal to open theswitch 325) and correspondingly reduces the variable attenuation (e.g.,by adjusting the signal on connection 265) to maintain a combinedattenuation in the network of attenuators 220. As further indicated inblock 610, the combined attenuation after the introduction of the fixedattenuation and the corresponding adjustment (i.e., reduction) of theattenuation provided by the variable attenuation generates a modifiedcompensated signal at the output of the compensator 230.

Once the fixed attenuator 322 is enabled by opening the switch 325 andthe variable attenuator 324 has been correspondingly adjusted by thecontroller 260, the comparator 250 is used to measure the differencebetween the first power level of the non-attenuated or received signaland a second power level of an attenuated and modified compensatedsignal to generate a second error signal, as indicated in block 612.Thereafter, as shown in block 614, the controller 260 generates acontrol signal that is a function of the first error signal and thesecond error signal and forwards the same to a control input of thevariable attenuator 324 by way of the DAC 270 to adjust the variableattenuator 324 in a manner that nullifies or substantially reduces anattenuation mismatch introduced by the fixed attenuator 322 and thevariable attenuator 324.

Those skilled in the art of power control systems as applied in RFtransmitters of the type commonly deployed in mobile cellular handsetscould readily adapt the present gain control system 200 and methods forcontrolling an adjustable power level for implementation in atransmitter or other suitable application.

While various embodiments of the gain control systems and methods forcontrolling an adjustable power level have been described, it will beapparent to those of ordinary skill in the art that many moreembodiments and implementations are possible. For example, the gaincontrol systems and methods for controlling an adjustable power levelare not limited to a specific type of radio transmitter or poweramplifier. Embodiments of the gain control systems and methods forcontrolling an adjustable power level are applicable to different typesof radio transmitters and power amplifiers and are applicable to anytransmitter that transmits a non-constant envelope signal. In addition,embodiments of the gain control systems and methods for controlling anadjustable power level are applicable to systems where a nearlycontinuous output signal power is desired.

What is claimed is:
 1. A system, comprising: a first power detectorconfigured to detect a power of a radio-frequency (RF) signal and toprovide a first power detector output; a network of attenuatorsconfigured to provide a fixed attenuation and a variable attenuation,the network of attenuators coupled to receive the RF signal and forwardan attenuated signal; a compensator configured to receive the attenuatedsignal and to provide gain to the attenuated signal in an amountproximate to the fixed attenuation to generate a compensated signal at acompensator output; a second power detector configured to detect a poweroutput of the compensated signal and to provide a second power detectoroutput; and a comparator configured to receive the first power detectoroutput and the second power detector output, and generate a first errorsignal.
 2. The system of claim 1 further comprising a controllerconfigured to direct the network of attenuators to controllably bypassthe fixed attenuation when the first error signal is generated.
 3. Thesystem of claim 2 wherein the controller is further configured toreceive the first error signal, enable the fixed attenuation,correspondingly adjust the variable attenuation, receive a second errorsignal responsive to the total attenuation from the combination of thefixed attenuation and the adjusted variable attenuation.
 4. The systemof claim 3 wherein the controller is further configured to provide acontrol signal to the network of attenuators as a function of the firsterror signal and the second error signal to nullify or reduce anattenuation mismatch introduced between the fixed attenuation and theadjusted variable attenuation.
 5. The system of claim 4 wherein thecontroller is configured to modify the control signal such that anoverall attenuation introduced by the network of attenuators before andafter enabling the fixed attenuator is about the same.
 6. The system ofclaim 4 wherein the controller includes a memory that stores the firsterror signal before enabling the fixed attenuation.
 7. The system ofclaim 4 further comprising an analog-to-digital converter (ADC)configured to receive the first error signal and the second errorsignal, the ADC configured to generate digital representations thereofthat are provided to the controller.
 8. The system of claim 4 furthercomprising: a digital-to-analog converter (DAC) configured to receivethe control signal and generate an analog representation thereof that isprovided to a control input that modifies the variable attenuation. 9.The system of claim 4 wherein an attenuation control range provided bythe controller and the variable attenuation is at least 5 dB greaterthan a step change provided by enabling the fixed attenuation.
 10. Thesystem of claim 1 wherein the first power detector and an input of thenetwork of attenuators are coupled to a modulator.
 11. The system ofclaim 1 wherein an output of the network of attenuators is coupled to apower amplifier.
 12. The system of claim 1 wherein the first and secondpower detectors are diode detectors.
 13. The system of claim 1 furthercomprising: a first low-pass filter coupled to the first power detectoroutput and a first input of the comparator; and a second low-pass filtercoupled to the second power detector output and a second input of thecomparator.
 14. A wireless device, comprising: a baseband subsystem; atransmitter in communication with the baseband subsystem, thetransmitter having a gain control system, the gain control systemincluding a first power detector configured to detect a power of aradio-frequency (RF) signal and to provide a first power detectoroutput; a network of attenuators configured to provide a fixedattenuation and a variable attenuation, the network of attenuatorscoupled to receive the RF signal and forward an attenuated signal; acompensator configured to receive the attenuated signal and to providegain to the attenuated signal in an amount proximate to the fixedattenuation to generate a compensated signal at a compensator output; asecond power detector configured to detect a power output of thecompensated signal and to provide a second power detector output; and acomparator configured to receive the first power detector output and thesecond power detector output, and generate a first error signal; and anantenna in communication with the transmitter and configured tofacilitate transmission of the RF signal.
 15. The wireless device ofclaim 14 further comprising a controller configured to direct thenetwork of attenuators to controllably bypass the fixed attenuation whenthe first error signal is generated.
 16. The wireless device of claim 15wherein the controller is further configured to receive the first errorsignal, enable the fixed attenuation, correspondingly adjust thevariable attenuation, receive a second error signal responsive to thetotal attenuation from the combination of the fixed attenuation and theadjusted variable attenuation.
 17. The wireless device of claim 16wherein the controller is further configured to provide a control signalto the network of attenuators as a function of the first error signaland the second error signal to nullify or reduce an attenuation mismatchintroduced between the fixed attenuation and the adjusted variableattenuation.
 18. The wireless device of claim 17 wherein the controlleris configured to modify the control signal such that an overallattenuation introduced by the network of attenuators before and afterenabling the fixed attenuator is about the same.
 19. The wireless deviceof claim 17 wherein the controller includes a memory that stores thefirst error signal before enabling the fixed attenuation.
 20. Thewireless device of claim 17 further comprising an analog-to-digitalconverter (ADC) configured to receive the first error signal and thesecond error signal, the ADC configured to generate digitalrepresentations thereof that are provided to the controller.
 21. Thewireless device of claim 17 further comprising: a digital-to-analogconverter (DAC) configured to receive the control signal and generate ananalog representation thereof that is provided to a control input thatmodifies the variable attenuation.
 22. The wireless device of claim 17wherein an attenuation control range provided by the controller and thevariable attenuation is at least 5 dB greater than a step changeprovided by enabling the fixed attenuation.
 23. The wireless device ofclaim 14 wherein the first power detector and an input of the network ofattenuators are coupled to a modulator.